Optical Modulation Of Quasi-bound State In Continuum Based On Dirac Semi-metallic Metameterials

The bound state in the continuum（BIC）is a mathematical concept with an infinite quality（Q）factor,which exists only in the ideal infinite array structure.When the external perturbation is introduced,the ideal BIC can be leaked into quasi-BIC with high Q factor,and a sharp resonance shape can be observed in the spectrum.The electromagnetic or light waves can effectively be restricted in the structure by using quasi-BIC excited mechanism in metamaterials,which makes them have attractive prospects in lasers,sensors,modulators and absorbers.However,the quasi-BIC modes in traditional metals or dielectric metamaterials are often confronted with problems such as non-dynamic modulation or large mode volume.In this paper,BIC is introduced into bulk Dirac semimetal（BDS）metamaterial,and the optical modulation effect of BDS metamaterial is studied by using the dynamic adjust dielectric constant of BDS.The research contents are as follows:1)A pair of BDS square resonators is designed.The BIC can be evolved into a quasi-BIC with a high Q factor by breaking the C₂ symmetry of the structure,and the Q factor is inversely proportional to the asymmetric parameters.The near field distribution shows a magnetic quadrupole resonance mode.The transmittance of the metamaterial can be effectively modulated by adjusting the Fermi energy of BDS,the maximum transmission difference is up to 82%,and the resonance frequency is almost unchanged.The physical mechanism behind it is that the real part of refractive index of BDS remains unchanged while the imaginary part increases sharply with the increase of Fermi energy near the resonance frequency.In addition,the LC equivalent circuit analysis of the metamaterial shows that the theoretical prediction is in good agreement with the simulation results.The research results can provide theoretical support for the design of optical modulator.2)A pair of BDS nanorods arrays is proposed to study the physical evolution of quasi-BIC mode when BDS behaves as dielectric in the range of 60～70 THz.The results show that sharp resonance lines appear in the spectrum,and the near field distribution of quasi-BIC is dipole mode.When the Fermi energy of BDS is increased from 0.15 e V to 0.2 e V,the resonance line gradually disappears and the metamaterial is almost transparent to the light field.When Fermi energy continues to be increased to 0.3 e V,sharp resonance lines appear again in the spectrum almost at the same frequency,and its near field distribution shows an electric quadrupole resonance mode.This work has a certain application potential in optical modulation and optical switching devices.